Optical radiation measurement apparatus

ABSTRACT

An optical radiation measurement apparatus is provided. The apparatus has at least one radiation detector for measuring electromagnetic radiation emitted from at least two radiation sources. Separate radiation channels are provided in a channel member in order to provide a radiation path between the radiation sources and the radiation detector, which is common to all of the radiation sources.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an optical apparatus having atleast one radiation deflector for measuring electromagnetic radiationemitted from at least two radiation sources.

[0002] Apparatus of this type are known, for example, in conjunctionwith rapid heating furnaces for the thermal treatment of semiconductorsubstrates for manufacturing semiconductor chips. In order to be able tomeasure the parameters and characteristics, such as the temperature, theemissivity, the reflectivity, the transmissivity and/or thecharacteristics or thickness of a layer that is to be applied to thesemiconductor substrate during the thermal treatment, the radiationcoming from the semiconductor substrate is measured as is the radiationthat is emitted from the radiation sources provided for heating up thesemiconductor substrates. By comparing the two measured radiation valuesit is possible to differentiate between the radiation emitted from thesemiconductor substrate and the reflected radiation. Apparatus andmethods of this type are known, for example, from U.S. Pat. No.5,490,728, where light lines are used in order to guide the respectiveradiation, and in particular also the radiation given off by theradiation sources, to radiation detectors. The inlet openings of theselight lines, however, have a large and undefined opening angle, so thatalso a relatively great amount of background radiation is taken in andfalls upon the radiation detector. As a consequence, the measuredvalues—if at all—indicate little and are not specific with respect tothe actual radiation coming from the radiation sources.

[0003] Furthermore, from DE 93 12 231 an apparatus for measuring UVradiation is known where a photo diode for measuring UV radiationemitted from a radiation source is provided in a cylindrical housinghaving an opening. The opening is partially closed off by a restrictorthat forms a radiation channel.

[0004] Reference is further made to DE 31 29 065, which discloses adevice for the photoelectric monitoring of a flow medium, where a lightsource and a direct light receiver disposed opposite the light sourceare provided and the light receiver is disposed in a receiver bus havinga light line channel. DE 39 08 627 furthermore discloses a multi-elementinfrared detector where in front of each detector element there isdisposed a light line in the form of light conducting channels formed ina channel plate, with the dimensions of the channels effecting adampening of radar radiation. In addition, disposed in front of thechannel plate is a shutter or aperture plate which has openings that arealigned with the light conductive channels and have non-reflective innersurfaces. FR 2 707 005 finally discloses a semicircular photo detectorarrangement where light conducting channels are disposed in asemicircular carrier member, and a respective photo detector is providedat the ends of the light channels.

[0005] It is therefore an object of the present invention to provide anoptical radiation measurement apparatus which with straightforward meansenables a substantially more precise determination of theelectromagnetic radiation emitted from the radiation sources.

[0006] Starting from an optical radiation measurement apparatus of theaforementioned general type, this objective is inventively realized byseparate radiation channels formed in a channel member for the radiationpath between the radiation sources and the radiation detector, which iscommon for the radiation sources. The radiation channels can thereby bedesigned very precisely to the radiation source, so no, or only aninsignificant portion of, background radiation, which would falsify themeasurement result, strikes the radiation detector. As a result, theparameters, characteristics and intensities of the electromagneticradiation emitted from the radiation sources can be determinedsignificantly more precisely and more reliably.

[0007] Pursuant to one particularly advantageous specific embodiment ofthe invention, the radiation channel has a cross-sectional shape thatcorresponds to the shape of the radiation source. Due to this shape ofthe channel cross-section, and the dimensions thereof, a preciseadaptation of the radiation channel to the radiation source is possible,so that independently of the shape of the radiation source thebackground radiation can be reliably masked out.

[0008] It is particularly advantageous if the radiation channel has across-sectional shape that permits a radiation passage to the radiationdetector even if the radiation source deviates from the ideal position.As a result of such a formation of the channel, mechanical modificationsor deviations in position of the radiation source, for example a lampfilament, which occur, for example, by vibrations, being out ofadjustment, or deformations, for example during the heating process, arenot reflected in signal alterations that could otherwise adverselyaffect the measurement result and the evaluation.

[0009] It is particularly advantageous if the radiation channel, or atleast one wall of the radiation channel, is structured, for examplehaving a wavy, grooved or corrugated, or irregular wall structure. As aresult, the radiation that does not enter parallel to the axis of theradiation channel, in other words which does not originate from theradiation source, is also not guided by reflection upon the radiationdetector, but rather is adsorbed. The structured channel wall thereforeadditionally contributes to undesired and undefined background radiationand scatter light from not falling upon the radiation detector andthereby falsifying the measurement results.

[0010] Very advantageous is furthermore an embodiment of the inventionpursuant to which the radiation channel has at least one mechanism foraltering the cross-sectional area of the radiation channel. By alteringthe cross-sectional area of the channel, the intensity, with which theradiation given off by a radiation source strikes the radiationdetector, can be adjusted, which is especially advantageous if pursuantto a further specific embodiment of the invention, where a number ofradiation sources are present, the relationship of the radiation of therespective lamps that strikes the radiation detector can be adjustedrelative to one another by altering the cross-sectional area of therespective channel. A particularly straight forward mechanism foraltering the cross-sectional area of the channel, and hence of theradiation intensity that strikes the radiation detector, is a screw thatcan be screwed into the radiation channel transverse to the direction ofradiation. However, a variable aperture can also be used.

[0011] With some rapid heating systems for the thermal treatment ofsemiconductor substrates, cool air is blown in between the radiationsources in order to cool some of the elements, for example a reactionchamber. However, due to this cool air flow turbulances occur betweenthe radiation channels and the individual radiation sources and leads tofluctuations in intensity. In order to avoid these fluctuations inintensity, the channel member, with the radiation channel or channels,extends up to the radiation source or sources.

[0012] Pursuant to one preferred specific embodiment, the radiationchannel can be extended by at least one light transmissive intermediateelement that extends the radiation channel and is disposed between atleast one outlet opening of a radiation channel and an associatedradiation source, without the channel body having to be guided to justbefore the radiation source. In this connection advantageously anintermediate element that in common extends a plurality of radiationchannels is provided. Pursuant to one preferred embodiment of theinvention, a quartz or sapphire rod is used for the extension, withwhich reflections are to the greatest extent possible suppressed at theinner walls so that only the light coming directly from the radiationsource strikes the detector.

[0013] Pursuant to one particularly advantageous embodiment of theinvention—as already mentioned—a plurality of radiation sources aredisposed next to one another, and the channel member, for each radiationsource, has a separate radiation channel that extends to the commonradiation detector. The radiations of the individual radiation sources,accompanied by the exclusion of background radiation and reciprocalinfluence, are thereby reliably guided to the common radiation detector,thereby increasing the precision of measurement. If the radiationsources are, for example, individual lamps that are disposed next to oneanother in a row in the form of a lamp bank, as is the case, forexample, with rapid heating apparatus for the thermal treatment ofsemiconductor substrates, the channels are formed in a fan-like fashionin the channel member between the lamps and the common radiation source.

[0014] Since the lamps are essentially disposed in a row, pursuant to afurther embodiment of the invention a cylindrical lens is disposedbetween the ends of the radiation channels that face the radiationdetector and the radiation detector, with the lens focusing on theradiation detector the radiation of the individual radiation sourcesthat in a fan-like fashion feeds the radiation detector.

[0015] The inventive radiation measurement apparatus can be used withgreat advantage in conjunction with a rapid heating furnace for thethermal treatment of semiconductor substrates.

[0016] The invention will be explained subsequently with the aid of onepreferred embodiment where the radiation measurement apparatus is usedin conjunction with a rapid heating furnace for the thermal treatment ofsemiconductor substrates and in conjunction with the drawings, whichshow:

[0017]FIG. 1 a schematic longitudinal sectional illustration through arapid heating furnace utilizing the inventive radiation measurementapparatus,

[0018]FIG. 2 a cross-sectional view along the line II-II in FIG. 1,

[0019]FIG. 3 an enlarged schematic cross-sectional illustration of theradiation channel member illustrated in FIGS. 1 and 2,

[0020]FIG. 4 a cross-sectional illustration taken along the line IV-IVin FIG. 3,

[0021]FIG. 5 a partial cross-sectional illustration of the radiationchannel member looking in the direction of the narrow side of theradiation channel member that faces the lamps,

[0022]FIG. 6 an enlarged partial illustration of the radiation channelmember to explain the orientation and arrangement of the radiationchannels relative to a lamp, and

[0023]FIG. 7 an enlarged partial illustration of the region between anoutlet opening of a radiation channel and a radiation source to explaina further exemplary embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] The rapid heating furnace illustrated in FIGS. 1 and 2 has ahousing 1 on the upper and lower inner wall of which are respectivelymounted a bank 4, 5 of lamps comprising a number of individual lamps orindividual lamp tubes 2, 3, with these banks of lamps heating up asemiconductor wafer 6 that is disposed in a reaction chamber 7 in thehousing 1 between the banks 4, 5 of lamps.

[0025] The reaction chamber 7 is advantageously essentially comprised ofa material that is essentially transparent for the lamp radiation, andthat is also transparent with respect to the measuring wavelengths orthe measuring wavelength spectra of the pyrometer or the radiationdetectors that are used. With quartz glasses and/or sapphire, which havean absorption coefficient, averaged over the lamp spectrum, of about 0.1cm⁻¹ to 0.001 cm⁻¹, suitable reaction chambers for rapid heating systemscan be constructed where the thickness of the reaction chamber wall canbe between 1 mm and several centimeters, for example 5 cm. Dependingupon the thickness of the reaction chamber wall, the selection of thematerial can be effected with regard to the absorption coefficient.

[0026] Chamber walls having thicknesses in the range of centimeters arethen required in particular if in the reaction chamber 7 a vacuum (up tothe ultra-high vacuum) or an overpressure is to be generated. If thediameter of the reaction chamber is, for example, about 300 mm, thenwith a quartz glass thickness of about 12 mm to 20 mm an adequatemechanical stability of the chamber 7 is achieved, so that this chambercan be evacuated. The thickness of the reaction chamber wall is designedin conformity with the material of the wall, the size of the chamber,and the pressure loads.

[0027] The lamps are preferably halogen lamps, the filaments of which atleast partially have a helical or coiled structure. By means of an atleast partial helical structure, advantageously a specific predefinedgeometrical and spectral radiation profile of the lamp can be achieved.In this connection, the filament of the lamp can, for example,alternately include coiled and uncoiled filament sections. The radiationprofile (not only the geometrical but also the spectral) is in this caseessentially determined by the spacing between adjacent coiled filamentsections. A further possibility for defining the lamp radiation profileconsists, for example, in varying the density of the filament structure(for example the coil density) along the filament.

[0028] If the lamp profile is to be controllable, advantageously lamps,preferably rod lamps, having a number of individually controllablefilaments can be used. Lamps with controllable lamp profile areparticularly advantageous in rapid heating units for the thermaltreatment of large-surface substrates, for example 300 mm semiconductorwafers, since with these lamps and a suitable lamp control mechanism avery homogeneous temperature profile can be achieved along the surfaceof the substrate. As a consequence of the superposition of theindividual radiation profiles of the filaments there results an overallradiation profile of the lamp that is controllable over a wide range. Inthe simplest case, for example a halogen lamp, such a lamp includes twofilaments, for example each with a helical structure or an at leastpartially coiled structure, whereby the coil density and/or the spacingbetween the coiled filament sections of the first filament increasesfrom the first end to the second end of the lamp, and the coil densityand/or the spacing of the coiled element sections of the second filamentcorrespondingly decrease in the reverse order from the first to thesecond end of the lamp. The overall radiation profile can thus be variedover a wide range by the selection of the current strength in the twofilaments. A further possibility for embodying a lamp with controllableradiation profile consists in providing the filament of the lamp with atleast three electrical connections, whereby between each two connectionsdifferent operating voltages are applied. In this way, the filamenttemperature, and hence the radiation characteristic of a lamp, can becontrolled along sections of the filament.

[0029] As an alternative to the previously described lamps, plasma orarc lamps can also be used, whereby here also the radiation profile canbe controlled. Thus, for example, the lamp spectrum can be adjusted viathe current density from the UV region up to the near infrared.

[0030] From FIG. 2 it can be seen that a wafer pyrometer 8, which isdisposed on the underside of the housing 1, measures electromagneticradiation, which is emitted and reflected from the wafer 6, via a smallopening 9 that preferably, however not necessarily, is formed in thecenter of the wafer 6 that is to be treated in a wall of the housing.However, it is also possible to use a plurality of wafer pyrometers thatare disposed parallel to the axis of the lamp.

[0031] Apparatus of the previously described type are known, forexample, from U.S. Pat. No. 5,490,728. Furthermore, such a device isdescribed in the non-published DE 197 37 802 A and in DE 197 54 386.3 ofthe applicant and having the same filing date, which in order to avoidrepetition are incorporated by reference to the extent relevant to thepresent specification.

[0032] Disposed on the underside of the rapid heating furnace is aninventive optical radiation measurement apparatus that comprises apyrometer 10 and a channel member 11, in which are formed or moldedradiation channels 12, as will be discussed in detail subsequently withthe aid of FIGS. 3 to 5.

[0033] As can be seen in FIGS. 1 to 5, when viewed in a longitudinalsection the channel member 11 has the shape of a fan, which incross-section is disc or plate shaped. The channel member 11 is disposedin a corresponding recess 13 in the upper or lower wall of a housing,and is fastened to the housing 1. On that side of the channel member 11facing away from the lamp bank 5 an optical lens 14, preferably acylinder lens, is disposed in such a way that its focal point is locatedat or in the vicinity of a position at which the axes of the radiationchannels 12 intersect, so that the radiation that strikes the opticallens 14 enters the pyrometer 10.

[0034] As can be best seen in FIG. 1, the radiation channels 12 areformed or orientated in the channel member 11 in such a way that therespective filaments 15 of the individual lamps 3 lie on the extendedlongitudinal axes 16 of the respective radiation channel 12. Thepyrometer 10 or its optical lens 14 therefore precisely “sees” therespective lamp filament 15, as a result of which background radiation,which does not come from the lamp filament 15,—if at all—is only anegligibly small percentage of the entire light that falls upon thepyrometer 10.

[0035] The channel member 11 is shown enlarged in FIG. 3. From here, itcan be seen that the walls of the radiation channels 12 are structured,for example are provided with small curved portions that preventscattered radiation from reaching the pyrometer 10. The radiationchannels 12, with appropriate structuring, are formed in the channelmember 11 by means of milling.

[0036] Disposed in the vicinity of those ends of the radiation channels12 that face the pyrometer 10 are respective screws 16′ that can bescrewed to a greater or lesser degree into the radiation channels 12 andthereby alter the diameter of the radiation channels 12, so that theintensity of the radiation passing through the respective radiationchannel 12 can be altered or adjusted. As a result, it is possible toessentially set every desired relationship between the radiationintensities of the individual lamps 3 that fall upon the pyrometer 10.

[0037] Provided that the lamps respective have the same radiationintensity, more radiation intensity reaches the pyrometer 10 via theradiation channel 12 disposed the closest to the central axis 17 of thechannel member 11 than does via the more outwardly disposed radiationchannels 12. In order to compensate for this, the cross sectional areaof the more inwardly disposed radiation channels 12 can be made smallerby screwing the screws 16′ in further, thereby balancing the differentradiation intensities that fall upon the pyrometer 10. Every desiredrelationship of the radiation intensities relative to one another canalso be set in this manner.

[0038] As schematically illustrated in the exemplary embodiment of FIG.6, the diameters or cross-sectional areas of the radiation channels 12are optimally adapted to the shape of the lamps 3 or their elements 15,which contributes to further reducing the background or scatteredradiation that falls upon the pyrometer 10. The orientation of thechannel 12 in the channel member 11 or the channel window in the channelmember 11 is pursuant to FIG. 6 selected with regard to dimensions insuch a way that the filament is still disposed within the channel window18 even if the filament 15 vibrates or oscillates, or becomes deformedfor example during the heating process. This ensures that the lightintensity that falls upon the lamp pyrometer 10 is not altered byoscillations, vibration or deformations of the filament 15, and themeasurements and precision of measurements are not adversely affected.

[0039] In general, the radiation sources and/or the radiation channelsare preferably disposed in such a way that the lamp pyrometer signalresults from a lamp or filament section that is free of filament holdingmechanisms or other means that adversely affect the radiation flux orthe temperature of the filament or lamp portion observed through theradiation channels.

[0040] Whereas the lamp pyrometer 10 has optical lenses 14 withcylindrical lenses, the wafer pyrometer 8 (FIG. 2) can be provided witha round lens, a cylindrical lens or other lens-like means (e.g. zoneplates, Fresnel lenses), whereby the means can be correlated inconformity with the radiation geometry of a lens. It is, for example,for a lamp bank of parallel rod lamps advantageous to utilize a cylinderlens with a cylinder axis orientated parallel to the lamps. In general,in this way as large a space as possible, and hence for example ahemispherical reflection of the wafer 6, is measured in an as unlimiteda fashion as possible.

[0041]FIG. 7 shows a further exemplary embodiment of the presentinvention wherein an intermediate element 20, such as a quartz orsapphire rod, which extends the radiation channel 12, is disposedbetween the exit opening of the radiation channel 12 and the lamp 3. Thepurpose of this element 20 is to extend the radiation channel to justbefore the lamp, whereby the gap between the end of the element and thelamp is of the order of only a few millimeters. This prevents that flowturbulence that can occur between the exit opening of the respectivechannel 12 and the associated lamp 3 generate fluctuations in intensityduring the measurement process.

[0042] Although the extension element 20 is illustrated as a rod, it isalso possible to dispose a single quartz element over the entire rangeof the fan between the wall of the housing and the lamps. It is alsopossible to extend the fans to shortly before the lamps.

[0043] The present invention has in the aforegoing been described inconjunction with one preferred exemplary embodiment. To one skilled inthe art a number of modifications and embodiments are possible withoutdeviating from the inventive concept. For example, the use of theinventive optical radiation measurement apparatus is not limited torapid heating systems for the thermal treatment of wafers. Dependingupon the arrangements, forms and embodiments of the radiation sources,other channel member shapes in addition to fan shapes are possible. Inaddition, the configuration of the radiation channels 12 is not limitedto the specific embodiment illustrated in FIG. 3.

[0044] The specification incorporates by reference the disclosure ofGerman priority document 197 54 385.5 of Dec. 8, 1997, 198 28 135.8 ofJun. 24, 1998 and 198 52 321.1 of Nov. 12, 1998.

[0045] The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

What we claim is:
 1. An optical radiation measurement apparatuscomprising: at least two radiation sources; at least one radiationdetector for measuring electromagnetic radiation emitted from said atleast two radiation sources; and a channel member in which are providedseparate radiation channels to provide a radiation path between saidradiation sources and said radiation detector, which is common to all ofsaid radiation sources.
 2. An apparatus according to claim 1 , whereinsaid radiation channels have a cross-sectional shape that corresponds toa shape of said radiation sources.
 3. An apparatus according to claim 1, wherein said radiation channels have a cross-sectional shape thatpermits a radiation passage to said radiation detector even if saidradiation sources deviate from an ideal position thereof.
 4. Anapparatus according to claim 1 , wherein at least one wall of saidradiation channels is structured.
 5. An apparatus according to claim 4 ,which includes at least one means for varying the cross-sectional areaof at least one of said radiation channels.
 6. An apparatus according toclaim 5 , wherein said means for varying a cross-sectional area of saidradiation channels comprises a screw that can be screwed into aradiation channel transverse to a direction of radiation.
 7. Apparatusaccording to claim 1 , wherein a plurality of radiation sources aredisposed next to one another and said channel member, for each of saidradiation sources, has a separate radiation channel that is directedtoward said radiation detector.
 8. An apparatus according to claim 1 ,wherein said channel member, with said radiation channels, extends tosaid radiation sources.
 9. An apparatus according to claim 1 , whereinat least one light transmissive intermediate element, which extends atleast one of said radiation channels, is disposed between at least oneoutlet opening of said radiation channel and an associated radiationsource.
 10. Apparatus according to claim 9 , wherein said intermediateelement in common extends a plurality of radiation channels.
 11. Anapparatus according to claim 9 , wherein said intermediate element is aquartz or sapphire element.
 12. An apparatus according to claim 7 ,wherein said radiation sources are individual lamps that are disposednext to one another in a row as a lamp bank and wherein said radiationchannels are disposed in a fan-like fashion in said radiation memberbetween said lamps and a common radiation detector
 10. 13. An apparatusaccording to claim 7 , wherein a relationship of the radiation ofrespective lamps that strikes said radiation detector relative to oneanother can be adjusted by means of a mechanism that can vary across-sectional area of a respective radiation channel.
 14. An apparatusaccording to claim 1 , wherein a cylindrical lens is disposed betweensaid radiation detector and ends of said radiation channels that facesaid radiation detector.
 15. An apparatus according to claim 1 , for usein conjunction with a rapid heating system for the thermal treatment ofsemiconductor substrates.
 16. An apparatus according to claim 15 , whichincludes a reaction chamber within which is effected said thermaltreatment of said semiconductor substrate, said reaction chamberessentially comprising a material that is transparent for theelectromagnetic radiation of said radiation sources and for a spectrumof measurement wavelengths of said at least one radiation detector. 17.An apparatus according to claim 16 , wherein said transparent materialis at least one of the group consisting of quartz glass and sapphire.18. An apparatus according to claim 16 , wherein said material has anabsorption coefficient, averaged over a lamp spectrum, between 0.001cm⁻¹ and 0.1 cm⁻¹.
 19. An apparatus according to claim 16 , wherein saidreaction chamber has a wall thickness of between 1 mm and 5 cm.
 20. Anapparatus according to claim 1 , wherein said radiation sources compriseat least one filament having an at least partially coiled filamentstructure.
 21. An apparatus according to claim 20 , wherein the filamentstructure of said radiation sources results in a predefined geometricand spectral radiation profile.
 22. An apparatus according to claim 21 ,wherein said filament of said radiation source has an alternating coiledand uncoiled filament structure.
 23. An apparatus according to claim 21, wherein said radiation source has two individually controllablefilaments.
 24. An apparatus according to claim 20 , wherein at least onefilament has at least three electrical connections.
 25. An apparatusaccording to claim 1 , wherein said radiation source comprises at leastone halogen lamp or at least one arc lamp.
 26. An apparatus according toclaim 20 , wherein a density of at least one filament structure variesalong said filament.
 27. An apparatus according to claim 1 , whereinsaid radiation sources and said radiation channels are arranged relativeto one another such that said at least one radiation detector generatesa signal that is free of influences from filament holding mechanisms orother means that adversely affect radiation flux or a radiationtemperature of said radiation sources.